1. Field of the Invention
The present invention relates to switching voltage regulators. More particularly, the present invention relates to a switching voltage regulator comprising a cycle comparator for dynamic voltage scaling.
2. Description of the Prior Art
Prior art switching voltage regulators (such as discontinuous buck voltage regulators) may implement dynamic voltage scaling in order to optimize power consumption by using critical path gate speed as the feedback for switching control. Various techniques have been disclosed for measuring the critical path gate speed, including the incorporation of a ring oscillator that generates an oscillator signal with a frequency proportional to the gate speed of the critical path circuit (where the gate speed is inversely proportional to the propagation delay of the critical path circuit). The error between the oscillator frequency and a reference frequency represents the gate speed error used as feedback for switching control. In a discontinuous buck mode voltage regulator, an inductor charge cycle is triggered when the oscillator frequency falls below the reference frequency. Dynamic voltage scaling may be employed in any suitable application, for example, to optimize power consumption of a microprocessor that is configured to operate at different speeds depending on software dynamics, load dynamics, etc.
The frequency error is typically generated by computing the average of the oscillator frequency (e.g., using a counter), which introduces transport delay and quantization error into the feedback loop requiring appropriate compensation filtering (e.g., PID filtering). The compensation filtering typically reduces the bandwidth of the feedback loop which can lead to poor transient response. In systems where the gate speed of the critical path circuitry must not fall below an operating threshold, a margin is typically added (to the reference frequency) to compensate for a slow transient response of the voltage regulator. This added margin can lead to unnecessary power dissipation, which is of particular concern in portable applications. It is also desirable to minimize the ripple voltage of a switching voltage regulator in order to reduce power consumption while maintaining adequate transient response.
There is, therefore, a need to improve the transient response of a switching voltage regulator employing dynamic voltage scaling to reduce power consumption.